Power tool

ABSTRACT

The durability of a reduction mechanism is improved. An impact wrench includes a brushless motor, a sun gear rotatable by the brushless motor, a planetary gear meshing with the sun gear, an internal gear meshing with the planetary gear and having a first recess on an outer circumference, a gear case holding the internal gear and having a second recess on an inner circumference, a spindle holding the planetary gear, and a pin disposed in the first recess and in the second recess.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese PatentApplication No. 2019-002072, filed on Jan. 9, 2019, and Japanese PatentApplication No. 2019-181608, filed on Oct. 1, 2019, the entire contentsof which are hereby incorporated by reference.

BACKGROUND 1. Technical Field

The present invention relates to a power tool such as an impact driverand an impact wrench.

2. Description of the Background

Power tools such as impact drivers and impact wrenches each include amotor and an output shaft such as a spindle or an anvil. When the motoris driven, the output shaft rotates to perform operations such astightening screws or nuts.

In an impact driver described in Japanese Unexamined Patent ApplicationPublication No. 2016-97498, a spindle accommodated in a case includes acarrier in its rear portion for axially supporting a plurality ofplanetary gears. In this structure, the planetary gears, to which therotation of the motor is transmitted, allows the sun-and-planet motionof the planetary gears inside the internal gear, which is arrangedoutside the planetary gears. This causes the spindle to rotate at alower speed.

BRIEF SUMMARY

In a known power tool, shock applied to the spindle in an abnormalimpact force operation may be transmitted to the planetary gears and theinternal gear, thus possibly damaging these gears.

One or more aspects of the present invention are directed to improvingthe durability of a reduction mechanism of a power tool.

A first aspect of the present invention provides a power tool,including:

-   -   a motor;    -   a sun gear rotatable by the motor;    -   a planetary gear meshing with the sun gear;    -   an internal gear meshing with the planetary gear, the internal        gear having a first recess on an outer circumference;    -   a gear case holding the internal gear, the gear case having a        second recess on an inner circumference;    -   a spindle holding the planetary gear; and    -   at least one pin disposed in the first recess and in the second        recess.

A second aspect of the present invention provides a power tool,including:

-   -   a motor;    -   a sun gear rotatable by the motor;    -   a planetary gear meshing with the sun gear;    -   an internal gear meshing with the planetary gear, the internal        gear having a first recess on an outer circumference;    -   a gear case holding the internal gear, the gear case having the        second recess on an inner circumference;    -   a spindle holding the planetary gear; and    -   at least one pin disposed in the first recess and in the second        recess, the pin being elastically deformable when the internal        gear rotates with respect to the gear case.

A third aspect of the present invention provides a power tool,including:

-   -   a motor;    -   a sun gear rotatable by the motor;    -   a planetary gear meshing with the sun gear;    -   an internal gear meshing with the planetary gear;    -   a gear case holding the internal gear;    -   a spindle holding the planetary gear;    -   at least one tab member arranged on one of the internal ear or        the gear case;    -   at least one receiver arranged on the other of the internal gear        or the gear case to receive the tab member; and    -   at least one elastic piece located between the internal gear and        the gear case,    -   wherein the elastic piece deforms elastically in a        circumferential direction of the internal gear to allow the tab        member to come in contact with the receiver.

The above aspects of the present invention improve the durability of thereduction mechanism of the power tool.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an exploded perspective view of an impact wrench, a cover, anda side handle.

FIG. 2 is a longitudinal central sectional view of the impact wrench.

FIG. 3 is an enlarged sectional view of a body in FIG. 2.

FIG. 4 is a partial rear view of an impact wrench body.

FIG. 5A is a cross-sectional view taken along line A-A in FIG. 3, andFIG. 5B is a view of planetary gears taken along the same section in thedirection indicated by arrows.

FIG. 6A is a cross-sectional view taken along line B-B in NG. 3, andFIG. 6B is an enlarged view of area C.

FIG. 7A is a rear view of a spindle, FIG. 7B is a cross-sectional viewtaken along line D-D in FIG. 7A, FIG. 7C is a cross-sectional view takenalong line E-E in FIG. 7A, and FIG. 7D is a cross-sectional view takenalong line F-F in FIG. 7A.

FIG. 8 is an enlarged sectional view of a body of an impact wrenchaccording to a modification.

FIG. 9 is a cross-sectional view taken along line G-G in FIG. 8.

FIG. 10 is a cross-sectional view taken along line H-H in FIG. 8.

FIG. 11A is a rear view of a spindle according to the modification, FIG.11B is a cross-sectional view taken along line I-I in FIG. 11A, FIG. 11Cis a cross-sectional view taken along line J-J in FIG. 11A, and FIG. 11Dis a cross-sectional view taken along line K-K in FIG. 11A.

FIG. 12 is an enlarged sectional view of a body of an impact wrenchaccording to another modification.

FIG. 13 is an exploded perspective view of a gear case and an internalgear.

FIG. 14A is a cross-sectional view taken along line L-L in FIG. 12, andFIG. 14B is a cross-sectional view taken along line M-M in FIG. 12.

DETAILED DESCRIPTION

Embodiments of the present invention will now be described below withreference to the drawings.

FIG. 1 is an exploded perspective view of an impact wrench as an exampleof a power tool, a cover, and a side handle. FIG. 2 is a longitudinalcentral sectional view of the impact wrench.

An impact wrench 1 includes a body 2 and a handle 3. The body 2 extendsin the front-rear direction. The handle 3 extends in the up-downdirection. The impact wrench 1 is T-shaped as viewed laterally. An anvil4 serving as an output shaft protrudes from a leading end of the body 2.A battery mount 5 is located at the lower end of the handle 3. Thebattery mount 5 receives a battery pack 6, which serves as a powersupply.

A housing for the body 2 includes a body housing 7 formed from asynthetic resin, and a metal hammer case 9. The body housing 7accommodates a brushless motor 8 in its rear portion. The handle 3extends from lower portion of the body housing 7. The hammer case 9 isattached in front of the body housing 7 to accommodate a spindle 10 anda striking mechanism 11. The body housing 7 is assembled by fastening apair of right and left half housings 7 a and 7 b with screws 12extending in right-left direction.

The body housing 7 contains a metal gear case 13 behind the hammer case9. The gear case 13 protrudes rearward, and is fitted with a rear end ofthe hammer case 9. The gear case 13 has four ribs 14 circumferentiallyprotruding at upper-right, upper-left, lower-right, and lower-leftpositions on its outer periphery. Behind the ribs 14, rear bosses 15 arelocated on the outer periphery of the front end of the body housing 7.In front of the ribs 14, front bosses 16 are located on the outerperiphery of the rear end of the hammer case 9. As shown in FIGS. 1 and4, the front bosses 16 receive bolts 17 screwed from the rear throughthe rear bosses 15 and the ribs 14, fastening the body housing 7, thegear case 13, and the hammer case 9 together. In this manner, the metalhammer case 9 receives the bolts 17, which firmly join the body housing7 and the hammer case 9 together and improve durability.

The hammer case 9 is cylindrical, and includes a case body 20, a taperedportion 21, and a front cylinder 22. The case body 20 has a graduallydecreasing diameter from a rear end toward the front. The taperedportion 21 is continuous with the front of the case body 20. The taperedportion 21 is tapered and has a diameter gradually decreasing with agreater inclination than the case body 20. The front cylinder 22 iscontinuous with the front of the tapered portion 21. The front cylinder22 has a uniform diameter in the front-rear direction. The taperedportion 21 has two concentrically protruding ring-shaped rear stoppers23A and 23B on its outer circumference. The tapered portion 21 also hasfour radial ribs 24 extending in the radial direction of the taperedportion 21 as viewed from the front at circumferentially equal intervalson its outer circumference. The radial ribs 24 are higher than the rearstoppers 23A and 23B.

The front cylinder 22 has a ring-shaped front stopper 25 in the middleof the outer circumference in the front-rear direction.

A cover 26 is externally mounted to the hammer case 9 from the front.The cover 26 is dividable into a rear first cover 27 and a front secondcover 28.

The first cover 27 is formed from rubber, and is externally mounted tocover a front end of the case body 20 and a rear half of the taperedportion 21. As shown in FIG. 3, the first cover 27 has, on its innercircumference at the front end, a ring-shaped engagement groove 29 thatis engaged with the rear stopper 23A. The first cover 27 has four rearaxial grooves 30 on its inner circumference. The front ends of the rearaxial grooves 30 communicate with the engagement groove 29. Each rearaxial groove 30 is engaged with the corresponding radial rib 24. Thefirst cover 27 has a cutout 31 on its lower portion. The cutout 31prevents interference with an extension 48 (described later) located onthe handle 3.

The second cover 28 is formed from a resin, and is externally mounted tocover a front half of the tapered portion 21 and the front cylinder 22.The second cover 28 includes a pair of half rings 28 a and 28 bdividable into right and left parts that are joined together with a ringspring 38 (described later). The second cover 28 has, on its innercircumference at the rear end, a ring-shaped rear positioning groove 32,which is engaged with the rear stopper 23B. A ring-shaped frontpositioning groove 33, which is engaged with the front stopper 25 on thefront cylinder 22, is formed in front of the rear positioning groove 32.The second cover 28 has four front axial grooves 34 on its innercircumference. Each front axial groove 34 communicates with thepositioning grooves 32 and 33, and is engaged with the correspondingradial rib 24 on the tapered portion 21. The second cover 28 has, on itsouter circumference, a fitting groove 35 to receive a side handle 40.The fitting groove 35 has a ring-shaped recessed groove 36 and fourrecesses 37 at circumferentially equal intervals. The ring spring 38 isexternally mounted on the recessed groove 36.

The first cover 27 is externally mounted to cover the case body 20 andthe rear half of the tapered portion 21 with the cutout 31 facingdownward and the rear axial grooves 30 aligned with the radial ribs 24on the tapered portion 21. The engagement groove 29 is positionedthrough engagement with the rear stopper 23A.

The second cover 28 is then externally mounted to cover the front halfof the tapered portion 21 and the front cylinder 22 with the half rings28 a and 28 b open laterally against the urging force from the ringspring 38. The half rings 28 a and 28 b are then joined with the ringspring 38 again. When the front axial grooves 34 are aligned with theradial ribs 24, the rear positioning groove 32 is positioned throughengagement with the rear stopper 23B and the front positioning groove 33is positioned through engagement with the front stopper 25, and thesecond cover 28 is fixed to the front cylinder 22. In this state, thefront end of the first cover 27 comes in contact with the rear end ofthe second cover 28, and is prevented from slipping frontward.

The side handle 40, which is detachable from the front cylinder 22, isattached to the front cylinder 22 with the second cover 28 beingattached to the front cylinder 22. The side handle 40 includes a lineargrip 41 and a clamp 42. The clamp 42 is a strip plate shaped into a ringand protrudes along the extension of the grip 41 in an expansible andcontractible manner. The clamp 42 has a plurality of protrusions 43protruding inwardly on the inner surface. Each protrusion 43 correspondsto the recess 37 on the second cover 28.

The expanded clamp 42 is externally mounted on the fitting groove 35 onthe second cover 28, and then is contracted with the protrusions 43aligned with the recesses 37. The side handle 40 is thus attached to thefront cylinder 22 with the clamp 42 clamping the front cylinder 22 withthe second cover 28 in between, and thus the grip 41 protrudes sidewardfrom the front cylinder 22.

The side handle 40 can be attached with the second cover 28 beingattached, without the need to remove the second cover 28.

The handle 3 has a switch 45 and a forward/reverse switch button 47 inits upper portion. The switch 45 has a trigger 46 protruding frontward.The forward/reverse switch button 47 switches the rotation of thebrushless motor 8. The body housing 7 has the extension 48 above thetrigger 46. The extension 48 covers the lower surface of the hammer case9 and extends more frontward than the trigger 46. The extension 48 has,on its distal end, a light source 49 including a light-emitting diode(LED) for illuminating the front of the anvil 4.

The battery mount 5 accommodates a controller 50 including a controlcircuit board 51. The control circuit board 51 includes, for example, aswitching element and a microcomputer for controlling the brushlessmotor 8. The control circuit board 51 includes a switch panel 52 having,for example, a button for selecting a striking force and a lamp forindicating the remaining battery capacity. The switch panel 52 isexposed on the front upper surface of the battery mount 5. In front ofthe switch panel 52, a projecting portion 54 is located at the front endof the battery mount 5. The projecting portion 54 accommodates a secondlight source 53 including an LED and facing upward.

The lower portion of the handle 3 and the battery mount 5 are connectedto each other by joining and fastening, with screws, right and left halfparts 5 a and 5 b. The right and left half parts 5 a and 5 b form thebattery mount 5 to a joint 55 protruding from the lower end of thehandle 3. An elastic material 56 is arranged between the joint 55 andthe battery mount 5 to reduce shock and vibration propagating from thehandle 3 to the battery mount 5.

The battery pack 6 is slid onto the battery mount 5 from the front andconnected to the battery mount 5 with rails fitting each other and ahook 57 engaged with the battery mount 5. When the battery pack 6 isconnected to the battery mount 5, terminals on a terminal mount 58included in the battery mount 5 are electrically connected to terminalson the battery pack 6 below the controller 50. A disengagement button 59is located below the projecting portion 54. The disengagement button 59switches the hook 57 in a disengagement state when the battery pack 6 isremoved.

The body 2 includes the brushless motor 8, the spindle 10, the strikingmechanism 11, and the anvil 4 in this order from the rear.

The brushless motor 8 is an inner-rotor motor including a stator 60 anda rotor 61 located in the stator 60. The stator 60 includes acylindrical stator core 62, a front insulator 63, a rear insulator 64,and six coils 65. The stator core 62 is formed by stacking multiplesteel plates. The front insulator 63 is arranged on the axially frontend face of the stator core 62, and the rear insulator 64 is arranged onthe axially rear end face of the stator core 62. The six coils 65 arewound around the stator core 62 via the front and rear insulators 63 and64. A sensor circuit board 66 and a short-circuiting member 67 arejoined to the rear insulator 64. The sensor circuit board 66 has threerotation detecting elements (not shown) to detect the positions ofpermanent magnets 72 on the rotor 61 and to output a rotationaldetection signal. The short-circuiting member 67 is formed by insertmolding three metal sheets 68. The three metal sheets 68 short-circuitfuse terminals, which are to be fused to wires between the coils 65,located diagonally from each other. The six coils 65 are wound inparallel and delta-connected using the short-circuiting member 67.

The stator 60 is held, on its outer circumference, by the support ribs69 each circumferentially protruding inward from the inner surfaces ofthe half housings 7 a and 7 b of the body housing 7. The half housings 7a and 7 b have, on their inner surfaces, projections (not shown) fittedwith recesses (not shown) located on the side surface of the rearinsulator 64.

The rotor 61 includes a rotational shaft 70 aligned with its axis, arotor core 71, and the four plate-like permanent magnets 72. The rotorcore 71, which is substantially cylindrical, surrounds the rotationalshaft 70, and is formed by stacking multiple steel plates. The permanentmagnets 72 are fixed inside the rotor core 71. The rear end of therotational shaft 70 is axially supported by a bearing 73 held in a rearportion of the body housing 7. The front end of the rotational shaft 70is axially supported by a bearing 75 held by a bearing holder 74 in thegear case 13. A sun gear 76 is formed at the front end of the rotationalshaft 70. The front end of the rotational shaft 70 protrudes frontwardfrom the gear ease 13. The rotational shaft 70 has a centrifugal fan 77behind the bearing 75. The body housing 7 has air outlets 78 on its twolateral side surfaces at positions corresponding to the centrifugal fan77. As shown in FIG. 4, the body housing 7 also has air inlets 79 on itsrear surface.

A space defined by the hammer ease 9 and the gear case 13 accommodatesthe spindle 10 and the striking mechanism 11. The spindle 10 is integralwith a carrier 81 having a rear portion holding four planetary gears 82and 83 (described later) with support pins 84. The spindle 10 has anaxial blind hole 85 at its rear end. The spindle 10 includes asmaller-diameter portion 86 at its front end.

As shown in FIGS. 7A to 7D, the carrier 81 includes a front plate 87,which is disk-shaped, a rear plate 88, and four connectors 89. The rearplate 88 is located behind and parallel to the front plate 87. Theconnectors 89 connect the front plate 87 and the rear plate 88. Thefront end of the support pin 84 is supported by the front plate 87, andthe rear end of the support pin 84 is supported by the rear plate 88.The support pins 84 hold the planetary gears 82 and 83. The rear plate88 has, on its outer circumference, an outer support 90 having adiameter greater than the perimeter of the bearing holder 74 in the gearcase 13. The outer support 90 protrudes rearward from the rear plate 88.The outer support 90 overlaps the bearing holder 74 in the radialdirection of the spindle 10. A bearing 91 between the outer support 90and the bearing holder 74 axially supports the rear end of the spindle10 from inside. In this state, the bearing 91 is located outward fromthe bearing 75, and radially overlaps the bearing 75. The outer support90 holds the bearing 91 along the entire periphery.

With the rear end of the spindle 10 supported by the bearing 91, the sungear 76 on the rotational shaft 70 is inserted into the blind hole 85from the rear. The front end of the spindle 10 is supported with thesmaller-diameter portion 86 coaxially inserted into an insertion hole108 extending along the axis of the anvil 4.

As shown in FIGS. 5A to 6B, the planetary gears 82 and 83 are locatedseparately. On two large and small concentric circles about the axis ofthe spindle 10, the two planetary gears 82 are located on the innersmall concentric circle, and the two planetary gears 83 are located onthe outer large concentric circle. The inner planetary gears 82 meshwith the sun gear 76 on the rotational shaft 70.

The outer planetary gears 83 each have two stages and include alarger-diameter portion 83 a and a smaller-diameter portion 83 b. Thelarger-diameter portion 83 a is located frontward and meshes with theinner planetary gear 82. The smaller-diameter portion 83 b is coaxialwith the larger-diameter portion 83 a and located behind thelarger-diameter portion 83 a. The smaller-diameter portion 83 b has asmaller diameter than the larger-diameter portion 83 a. Thelarger-diameter portion 83 a has a larger diameter and more teeth thanthe planetary gear 82, and meshes with the planetary gear 82. Thesmaller-diameter portion 83 b has a smaller diameter and fewer teeththan the planetary gear 82, and meshes with an internal gear 92 heldinside the gear case 13. As described above, the planetary gears 82 meshwith the sun gear 76, and the planetary gears 83 mesh with the internalgear 92, allowing double reduction with the single internal gear 92 andincreasing the gear ratio without changing the size of the internal gear92.

The internal gear 92 is restricted from rotation by eight pins 93A and93B (four pins 93A and four pins 93B). The eight pins 93A and 93B extendin the front-rear direction between the internal gear 92 and the gearcase 13 at circumferentially equal intervals. The four pins 93A arecolumnar and formed from rubber. The four pins 93B are columnar andformed from iron (e.g., high carbon chromium bearing steels such asSUJ). As shown in FIGS. 6A and 6B, the pins 93A and 93B are alternatelyarranged circumferentially, and are each fitted in a first recess 94 andin a second recess 95. The first recesses 94 with a semicircular crosssection are located on the outer surface of the internal gear 92. Thesecond recesses 95 with a semicircular cross section are located on theinner surface of the gear case 13. The internal gear 92 is locatedradially outward from the rear plate 88.

A portion of the first recess 94 receiving each pin 93B has a crosssection with a smaller arc than a semicircle, whereas a portion of thesecond recess 95 receiving each pin 93B has a cross section with alarger arc than a semicircle. The second recess 95 holds the pin 93B.The four first recesses 94 each receiving the pin 93B have an arc with alarger diameter than the outer diameter of the pin 93B. A space S isleft between the first recess 94 and the pin 93B held in the secondrecess 95.

Thus, with the four rubber pins 93A elastically deformed, the internalgear 92 is slightly movable circumferentially within the range in whichthe four iron pins 93B each come in contact with the first recess 94.When the pins 93A are sheared (broken), the pins 93B coming in contactwith the first recesses 94 can retain the internal gear 92 in anonrotatable manner.

The striking mechanism 11 includes a hammer 100, balls 101, and a coilspring 102. The hammer 100 is externally mounted on the front portion ofthe spindle 10. The balls 101 are located between the hammer 100 and thespindle 10. The coil spring 102 urges the hammer 100 frontward. Thehammer 100 has, on its front surface, a pair of tabs (not shown) thatare rotationally engageable with a pair of arms 103 at the rear end ofthe anvil 4. The balls 101 are each fitted in a cam groove 104 on theouter peripheral surface of the spindle 10 and in a cam groove 104 onthe inner peripheral surface of the hammer 100, allowing corotation ofthe spindle 10 and the hammer 100. The coil spring 102 is externallymounted on the spindle 10. The front end of the coil spring 102 isreceived in a ring groove 105 on the rear surface of the hammer 100. Therear end of the coil spring 102 abuts against the front surface of thecarrier 81. In a normal state, the coil spring 102 urges the hammer 100to an advanced position at which the tabs are engaged with the arms 103.

The anvil 4 is supported coaxially with the spindle 10 by a bearingmetal 106 held by the front cylinder 22. The anvil 4 is positioned atthe front with a regulation ring 107 between the front cylinder 22 andthe arms 103. The anvil 4 has the axial insertion hole 108 at its rearend. The insertion hole 108 receives the smaller-diameter portion 86 ofthe spindle 10.

In front of the bearing metal 106, a seal ring 109 is located betweenthe front cylinder 22 and the anvil 4. The anvil 4 has an attachmentportion 110 at its front end. The attachment portion 110 has arectangular cross section and receives a socket (not shown).

When the side handle 40 is attached to the front cylinder 22 via thesecond cover 28 in the impact wrench 1 according to the presentembodiment, an operator can support the impact wrench 1 by holding thehandle 3 with one hand and holding the grip 41 of the side handle 40with the other hand. The grip 41 may extend in the laterally oppositedirection, and may be tilted upward or downward, rather than extendingsideward. In this case as well, the protrusions 43 and the recesses 37are fitted to position the grip 41.

In this state, when the operator presses the trigger 46 with the handholding the handle 3, the switch 45 is turned on, and the power of thebattery pack 6 drives the brushless motor 8. More specifically, themicrocomputer in the control circuit board 51 receives, from therotation detection element in the sensor circuit board 66, a rotationdetection signal indicating the positions of the permanent magnets 72 inthe rotor 61, and determines the rotational state of the rotor 61. Themicrocomputer in the control circuit board 51 controls the on-off stateof each switching element in accordance with the determined rotationalstate, and applies a current through the coils 65 in the stator 60sequentially to rotate the rotor 61.

The rotation of the rotational shaft 70 allows the sun-and-planet motionof the planetary gears 82 in the carrier 81 about the sun gear 76, andthen allows the sun-and-planet motion of the planetary gears 83 eachmeshing with the planetary gear 82 inside the internal gear 92. Thisallows the spindle 10 to rotate at lower speed, causing the hammer 100to rotate with the balls 101. Thus, the anvil 4 engaged with the hammer100 also rotates, allowing tightening of, for example, a bolt with thesocket. Turning on the switch 45 allows the control circuit board 51 toturn on the light source 49 to illuminate the front of the socket and toturn on the second light source 53 to illuminate the socket from below.

When the bolt is tightened more firmly and the torque of the anvil 4increases, the hammer 100 retracts while rolling the balls 101 rearwardalong the corresponding cam grooves 104 against the urging force fromthe coil spring 102. When the tabs are disengaged from the arms 103, thehammer 100 advances while rotating by rolling the balls 101 frontwardalong the corresponding cam grooves 104 under the urging force from thecoil spring 102. Then, the tabs are re-engaged with the arms 103 tocause the anvil 4 to generate a rotational impact force (impact). Theimpact is intermittently generated repeatedly, tightening the bolt morefirmly.

When the anvil 4 receives shock from an abnormal impact force, therepulsive force from the anvil 4 impulsively pushes the hammer 100 backto the rear ends of the cam grooves 104 in the spindle 10. In thisstate, the shock may be transmitted to the planetary gears 82 and 83 inthe spindle 10 and the internal gear 92. The internal gear 92, which isheld by the rubber pins 93A, is rotated circumferentially by the elasticdeformation of the pins 93A to absorb the shock. This structure reducesshock on the planetary gears 82 and 83 and the internal gear 92.

The impact wrench 1 according to the present embodiment includes thebrushless motor (motor) 8, the anvil (output shaft) 4 driven by thebrushless motor 8, the hammer case (case) 9 accommodating a part of theanvil 4, the first cover 27 covering a part of the hammer case 9, andthe second cover 28 covering another part of the hammer case 9. The sidehandle 40 is attachable to the second cover 28. The side handle 40 isattachable or detachable without attaching or detaching the second cover28 to or from the front cylinder 22. This facilitates the attachment ofthe side handle 40, and prevents the second cover 28 from being lost.

In particular, the first cover 27 is formed from rubber, and the secondcover 28 is formed from a resin and located in front of the first cover27. The first cover 27 and the second cover 28 can thus reliably protecta workpiece that comes in contact with the hammer case 9, and preventsthe side handle 40 attached to the second cover 28 from rattling andimproves durability.

The first cover 27 is positioned through engagement with the rearstopper (positioning unit) 23A protruding on the outer surface of thehammer case 9. The second cover 28 is positioned through engagement withthe rear stopper (positioning unit) 23B and the front stopper(positioning unit) 25 protruding on the outer surface of the hammer case9. Thus, the first cover 27 and the second cover 28 are easilyattachable, and are less likely to rattle or be misaligned onceattached.

Although the first cover is formed from rubber and the second cover isformed from a resin in the present embodiment, both the covers may beformed from rubber or from a resin.

The structure for engagement with the hammer case may be modified asappropriate. For example, the first cover may have more positioningunits or the second cover may have fewer positioning units. The divisionof the cover is not limited to the structure described in the aboveembodiment, and may be modified in design as appropriate. For example,the first cover may be longer, the second cover may be longer, or boththe covers have their end faces overlapping each other. The first covermay entirely cover the rear portion of the hammer case.

The impact wrench 1 according to the present embodiment includes thebrushless motor (motor) 8, the anvil (output shaft) 4 driven by thebrushless motor 8, the hammer case (case) 9 accommodating a part of theanvil 4, and the second cover (cover) 28, which is formed from a resin,covering a part of the hammer case 9 and fixed with the ring spring(elastic member) 38. The side handle 40 is attachable to the secondcover 28. The side handle 40 can thus be attachable or detachablewithout attaching or detaching the second cover 28 to or from the frontcylinder 22. This facilitates the attachment of the side handle 40, andprevents the second cover 28 from being lost. Further, the second cover28 is fixed with the ring spring 38. The attached side handle 40 is thusless likely to rattle.

In particular, the hammer case 9 and the second cover 28 arecylindrical, and the ring spring (elastic member) 38 is externally woundaround the second cover 28. The second cover 28, which is formed from aresin, can thus be reliably fixed with the ring spring 38.

The first cover (rubber cover) 27 covers a part of the hammer ease 9behind the second cover 28. The first cover 27 and the second cover 28thus protect a workpiece that comes in contact with the hammer case 9.

More ring springs may be used, or the ring spring may have another shape(front-rear dimension and thickness). The ring spring may be located atthe front or rear end of the second cover, rather than in the middle.The elastic member may be a coil spring or a circlip, rather than a ringspring.

The impact wrench 1 according to the present embodiment includes thebrushless motor (motor) 8, the sun gear 76 rotatable by the brushlessmotor 8, the planetary gears 82 and 83 meshing with the sun gear 76, theinternal gear 92 meshing with the planetary gears 83, the gear case 13holding the internal gear 92, the spindle 10 holding the planetary gears82 and 83, and the bearing (first bearing) 91 located between the gearcase 13 and the spindle 10. The bearing 91 supports the spindle 10 onits outer circumference and the gear case 13 on its inner circumference.This structure eliminates the need to hold the rear end of the spindle10 on the outer circumference. The bearing 91 can be smaller, thusallowing radially compact design.

In particular, the gear case 13 includes the bearing holder (innersupport) 74 supported on the inner circumference of the bearing 91. Thespindle 10 includes the outer support 90 supported on the outercircumference of the bearing 91. The bearing holder 74 and the outersupport 90 overlap each other in the radial direction of the spindle 10.The spindle 10 including the outer support 90 does not extend longfrontward, thus maintaining axially compact design.

The gear case 13 holds the bearing (second bearing) 75 axiallysupporting the rotational shaft 70. The first bearing 91 is locatedradially outward from the second bearing 75, and radially overlaps thesecond bearing 75. The spindle 10 can thus be axially smaller althoughthe first bearing 91 is located behind the internal gear 92.

The bearing is not limited to a ball bearing, but may be, for example, aneedle bearing, or a bearing metal. A plurality of bearings may belocated in the axial direction.

The structure of the outer support of the spindle is not limited to thestructure described in the above embodiment and may be modified asappropriate. For example, the outer support may have a smaller diameterthan the carrier, or may not be a ring but may include arc-shaped wallsarranged on the same circle.

FIG. 8 shows another structure in which the bearing axially supports thegear case and a spindle. The same components as in the above embodimentare given the same reference numerals and will not be describedrepeatedly, and the components different from those in the aboveembodiment will be described.

In an impact wrench 1 shown in FIG. 8 according to a modification, acarrier 81 of a spindle 10A includes no rear plate and no connector. Asshown in FIGS. 9 to 11D, a pair of protruding portions 96 integral withand protruding rearward from the front plate 87 are located at twopoints that are symmetric to each other on the same circle about theaxis of the spindle 10A. A bearing 91 is held by holding recesses 97 onthe inner rear ends of the protruding portions 96. Thus, the front plate87 simply supports the front ends of the support pins 84 in acantilevered manner. The protruding portions 96 each have a peripherallyrecessed portion 98A along their inner periphery. The protrudingportions 96 each have a peripherally convexed portion 98B along theirouter periphery.

The impact wrench 1 according to the modification includes the brushlessmotor (motor) 8, the sun gear 76 rotatable by the brushless motor 8, theplanetary gears 82 and 83 meshing with the sun gear 76, the internalgear 92 meshing with the planetary gears 83, the gear case 13 holdingthe internal gear 92, the spindle 10A holding the planetary gears 82 and83, and the bearing 91 located between the gear case 13 and the spindle10A. The spindle 10A has the pair of protruding portions 96 protrudingtoward the bearing 91. The bearing 91 is located inside the protrudingportions 96. This structure thus eliminates the need to hold the rearend of the spindle 10A on the outer circumference, and thus allows thebearing 91 to be smaller. This allows radially compact design.

The number of protruding portions and their shapes are not limited tothose described in the above embodiment and may be changed asappropriate. Three or more protruding portions may be provided inaccordance with the specifications of the gears.

The impact wrench 1 according to the present embodiment includes thebrushless motor (motor) 8, the sun gear 76 rotatable by the brushlessmotor 8, the planetary gears 82 and 83 meshing with the sun gear 76, theinternal gear 92 meshing with the planetary gears 83, the gear case 13holding the internal gear 92, and the spindle 10 holding the planetarygears 82 and 83. The internal gear 92 has the first recesses 94 on itsouter circumference. The gear case 13 has the second recesses 95 on itsinner circumference. The pins 93A, which are each fitted in the firstand second recesses 94 and 95, reduce shock received by the spindle 10from, for example, an abnormal impact force. This structure reduces thelikelihood of the planetary gears 82 and 83 and the internal gear 92being damaged, and improves the durability of the reduction mechanism.

In particular, the four first recesses 94 each receiving the iron pin93B are larger than the portion of the pin 93B received in the firstrecess 94, providing the internal gear 92 with a clearance for allowingcircumferential movement. This structure effectively releases shock inthe circumferential direction of the internal gear 92.

The pins 93A are elastically deformable, and thus effectively reducecircumferential shock.

The elastically deformable pins 93A and the elastically undeformablepins 93B are used. The pins 93B can retain the internal gear 92 in anonrotatable manner when the pins 93A are broken.

The number of pins (the number of first and second recesses) is notlimited to that described in the above embodiment, and may be increasedor decreased. The pins may have any shape other than a columnar shape.Although the iron pins are held in the second recesses on the gear casein the present embodiment, the pins may be held in the first recesses onthe internal gear reversely. In this case, the spaces are left in thesecond recesses. Although the spaces may be left for all the pins ratherthan for the selected pins (four pins), the rubber pins may each come incontact with the recess earlier than the iron pins. The spaces may beeliminated.

When the pins and the recesses are shaped to reduce shock, the pins maybe formed from a material other than an elastic material, such asrubber. For example, all the pins may be elastically undeformable pins,such as iron pins, or elastically deformable pins.

FIGS. 12 to 14B show an impact wrench according to a modification usingno separate pins for retaining the internal gear 92 in a nonrotatablemanner.

In the present modification, the internal gear 92 integrally includesfour tab members 98 integral with and protruding rearward from its rearend face. Each tab member 98 is formed as an arc-shaped plate extendingalong a circle about the axis of the internal gear 92. The tab members98 are arranged on the same circle at equal intervals in thecircumferential direction of the internal gear 92.

The gear case 13 has, on its rear inner circumferential surface, fourreceivers 99 each receiving the tab member 98 from the front. Eachreceiver 99 is also formed in arc-shape to extend along the same circlealong which the tab members 98 are arranged. The receivers 99 arearranged on the same circle at equal intervals in the circumferentialdirection of the gear case 13. Each receiver 99 is larger in thecircumferential direction than the tab member 98. The tab member 98 andthe receiver 99 have a space (clearance) between them in thecircumferential direction when the tab member 98 is received in thereceiver 99.

The internal gear 92 is elastically held by the four rubber pins 93A.Each pin 93A has a square cross section and extends in the front-reardirection. Each pin 93A is fitted in one of the four first recesses 94on the outer circumferential surface of the internal gear 92 and in oneof the four second recesses 95 on the inner circumferential surface ofthe gear case 13. The first recess 94 and the second recess 95 arequadrangular cutouts to each receive a half of the pin 93A. The pins 93Aand the sets of the tab members 98 and the receivers 99 are alternatelyarranged in the circumferential direction of the internal gear 92.

In the present modification, the bearing 91 supporting the rear plate 88of the carrier 81 is arranged between the outer support 90 and the rearinner circumferential surface of the gear case 13, instead of betweenthe bearing holder 74 and the outer support 90. The bearing 75 and thebearing 91 radially overlap each other as well. As shown in FIG. 14B,each support pin 84 supporting the planetary gear 82 or 83 is hollow forweight reduction.

In this manner, the internal gear 92 is elastically held by the fourpins 93A inside the gear case 13. In this state, each tab member 98 andeach receiver 99 are not in contact with each other in thecircumferential direction of the internal gear 92, leaving a space inthe circumferential direction.

When the anvil 4 receives shock from an abnormal impact force, therepulsive force from the anvil 4 impulsively pushes the hammer 100 backto the rear ends of the cam grooves 104 in the spindle 10. The shock isthen transmitted to the planetary gears 82 and 83 in the spindle 10 andthe internal gear 92. The internal gear 92, which is held by the rubberpins 93A, is rotated circumferentially by the elastic deformation of thepins 93A to absorb the shock. This structure reduces shock on theplanetary gears 82 and 83 and the internal gear 92. When the pins 93Aelastically deform more, the tab members 98 circumferentially come incontact with the receivers 99, restricting further rotation of theinternal gear 92.

In this modification, the internal gear 92 includes the tab members 98,and the gear case 13 includes the receivers 99 to receive the tabmembers 98. The pins 93A (elastic pieces) are arranged between theinternal gear 92 and the gear case 13. As the pins 93A deformelastically in the circumferential direction of the internal gear 92,the tab members 98 circumferentially come in contact with the receivers99.

This structure reduces the likelihood of the planetary gears 82 and 83and the internal gear 92 being damaged, thus improving the durability ofthe reduction mechanism.

Additionally, the tab members 98 come contact with the receivers 99 asthe pins 93A deform elastically, which prevents the pins 93A frombreaking. Further, the structure according to the present modificationuses no iron pins for retaining the internal gear 92 in a nonrotatablemariner, and thus includes fewer components than the structure accordingto the embodiments described above.

Although the internal gear includes the tab members and the gear caseincludes the receivers in the above modification, the internal gear mayinclude the receivers and the gear case may include the tab membersreversely. The numbers of tab members and receivers to be used and theirshapes may be changed as appropriate.

The elastic piece may be a pin having a circular cross section, ratherthan a square cross section. The number of pins and their positions mayalso be changed.

The power tool is not limited to an impact wrench, but may be, forexample, an impact driver, a screwdriver, a hammer, or a hammer drill.

The power tool may be any other power tool including a reductionmechanism using a planetary gear, such as an impact driver and ascrewdriver other than an impact wrench. The internal gear may have areduction mechanism with multiple stages.

The planetary gears may not be two-stage gears as in the aboveembodiment, but all the planetary gears supported by the single carriermay mesh with the internal gear. The power tool may include a motordifferent from a blushless motor, or may use an alternating current.

REFERENCE SIGNS LIST

-   1 impact wrench-   2 body-   3 handle-   4 anvil-   5 battery mount-   6 battery pack-   7 body housing-   8 brushless motor-   9 hammer case-   10, 10A spindle-   11 striking mechanism-   13 gear case-   20 case body-   21 tapered portion-   22 front cylinder-   23A, 23B rear stopper-   25 front stopper-   26 cover-   27 first cover-   28 second cover-   29 engagement groove-   32 rear positioning groove-   33 front positioning groove-   35 fitting groove-   38 ring spring-   40 side handle-   41 grip-   42 clamp-   45 switch-   50 controller-   60 stator-   61 rotor-   70 rotational shaft-   74 bearing holder-   73, 75, 91 bearing-   76 sun gear-   81 carrier-   82, 83 planetary gear-   84 support pin-   90 outer support-   92 internal gear-   93A, 93B pin-   94 first recess-   95 second recess-   96 protruding portion-   97 holding recess-   98 tab member-   99 receiver-   100 hammer-   S space

What is claimed is:
 1. A power tool, comprising: a motor; a sun gearrotatable by the motor; a planetary gear meshing with the sun gear; aninternal gear meshing with the planetary gear, the internal gear havingfirst recesses on an outer circumference; a gear case holding theinternal gear, the gear case having second recesses on an innercircumference; a spindle holding the planetary gear; a first pin in oneof the first recesses and in one of the second recesses, the first pinbeing elastically deformable; and a second pin in another of the firstrecesses and another of the second recesses, the second pin beingelastically undeformable.
 2. The power tool according to claim 1,wherein the first recesses are larger than a portion of the first pin orthe second pin in the first recesses to leave a clearance forcircumferential movement of the internal gear.
 3. The power toolaccording to claim 1, wherein the first pin is made of rubber, thesecond pin is made of iron, and the first pin and the second pin arealternately arranged in a circumferential direction of the internalgear.
 4. The power tool according to claim 1, wherein the first pin iselastically deformable when the internal gear rotates with respect tothe gear case.
 5. The power tool according to claim 1, wherein the firstpin and the second pin are columnar.
 6. The power tool according toclaim 5, wherein the first recesses and the second recesses each have asemicircular cross section.
 7. The power tool according to claim 1,wherein the power tool includes four of the first pin and four of thesecond pin arranged in the circumferential direction of the internalgear.
 8. A power tool, comprising: a motor; a sun gear rotatable by themotor; a planetary gear meshing with the sun gear; an internal gearmeshing with the planetary gear, the internal gear including a tabmember on an end face of the internal gear in an axial direction; a gearcase holding the internal gear, the gear case including a receiver toreceive the tab member; a spindle holding the planetary gear; and anelastic piece between the internal gear and the gear case, wherein theelastic piece is deformable elastically in a circumferential directionof the internal gear to allow the tab member to come in contact with thereceiver.
 9. The power tool according to claim 8, wherein the tab memberand the receiver are arc-shaped to extend in a circumferential directionof the internal gear.
 10. The power tool according to claim 9, whereinthe internal gear includes four of the tab member, and the gear caseincludes four of the receiver, and the four tab members and the fourreceivers are arranged in the circumferential direction of the internalgear.
 11. The power tool according to claim 8, wherein the elastic piecehas a square cross section.
 12. The power tool according to claim 11,wherein the internal gear has a first recess on an outer circumference,the gear case has a second recess on an inner circumference, and theelastic piece is in the first recess and in the second recess.
 13. Thepower tool according to claim 11, wherein the power tool includes fourof the elastic piece arranged in the circumferential direction of theinternal gear.
 14. The power tool according to claim 11, wherein thepower tool includes the elastic piece and at least one set of the tabmember and the receiver that are alternately arranged in thecircumferential direction of the internal gear.